The patent EP0390882B1 discloses a rocking square piston with integrally mounted connecting rod; its unconventional design enables the asymmetric timing of the ports: the exhaust port opens first while the transfer port closes last, which is crucial for the emissions, the efficiency, the power output etc.
The patent U.S. Pat. No. 5,163,388 discloses a two stroke wherein a valve selectively opens and closes a pipe connecting the source of pressurized air/mixture with a port on the cylinder liner located at a “higher lever” as compared to the exhaust port, allowing the effective asymmetric timing of the engine: after the closing of the exhaust by the piston, the introduction of air/mixture into the combustion chamber continues.
With a pair of pistons per combustion chamber (as in the opposed piston engines) the timing of the ports can be asymmetric, in expense of the added complication and vibrations.
The DE1,576,249A1 (of Anscheidt) discloses a two-stroke engine with asymmetric intake: an elastic strip (or band) secured, at one end, at the small end of the connecting rod, opens and closes an intake piston port that cooperates with an inlet port on the cylinder. As the piston reciprocates, the connecting rod pivots about the wrist pin and the elastic strip deforms following the shape of the inner piston surface wherein it abuts, covering and uncovering the intake piston port. This way the communication of the crankcase with the inlet port starts early in the compression stroke (for instance 120 degrees before the TDC) and ends early in the expansion stroke (for instance 40 degrees after the TDC), being substantially asymmetric.
The PCT/GB95/02952 (of Keith Charles Sugden) claims “a piston with internal compartments characterized by being segregated with a partition which also forms the matting surface for the lower bearing of the connecting rod little-end which has not gudgeon pin and is housed inside the uppermost compartment in such shape and configuration that arc sliding of said bearing forms a gate-valve using said partition's one or more ports to permit air from the compartment fed from a pressurized air input to flow at designated crank positions through the open gate-valve into another compartment and from there into a transfer passage which then conducts the air through the cylinder wall appreciably above the exhaust port's opening level so that the combination of piston plus gate-valve motion subjects the cylinder plus transfer passage interiors to a repetitive fixed sequence of operational modes”.
The GB2,288,637 (of Keith Charles Sugden) claims “a cylinder with a piston slidably sealed in the cylinder, the cylinder including at least one transfer port and at least one exhaust port, with the said transfer port being connected into intermittent communication with the inlet manifold via a moving gate valve within the piston, the said valve operated and controlled by the relative arc motion occurring between the said piston and the constraining connecting rod”.
In the FR689,089 (of Mijnlieff) the top end of an unconventional connecting rod pivots on the piston crown and seals one side of the combustion chamber; the pivotal motion of the connecting rod relative to the piston enables a substantially asymmetric transfer and exhaust; sealing means (similar to the piston rings) are required between the piston and the connecting rod.